1. Field of the Invention
The present invention relates to improvements in pharyngeal airways of the type used during surgical and other medical procedures to prevent obstruction of the pharynal region of the alimentary canal, for example, while a patient is under anesthesia. More particularly, the invention relates to a pharyngeal airway which, in addition to being adapted to maintain a patient's airway open during a medical procedure, is also adapted to administer an inhalant gas (e.g., oxygen) and/or sample an expired gas, i.e., carbon dioxide in the patient's pharynx so as to provide an early indication of an interruption of proper respiration or breathing.
2. Discussion of the Prior Art
During surgical procedures in which a patient is placed under general anesthesia, an anesthetist or anesthesiologist continuously administers a general anesthetic (e.g. sodium pentothal/muscle relaxant) and manages the patient's respiration or breathing. Often, an endotracheal tube is fitted into the patient's trachea for administering anesthesia and other drugs, and a mechanical ventilator is used to pump oxygen into the patient's lungs and to extract therefrom expired carbon dioxide. To ensure that proper ventilation is taking place, it is common for the anesthetist to monitor the respective levels of (i) oxygen saturation in the patient's blood and (ii) the expired carbon dioxide. Pulse oximetry is the technique most often used to detect the level of blood oxygenation, and capnography is commonly used to monitor the expired carbon dioxide level. Of the two types of monitors for detecting proper ventilation, the carbon dioxide monitor is far quicker to indicate an interruption of ventilation since oxygen saturation can remain at a normal or near normal level for several minutes after proper ventilation has ceased. On the other hand, an interruption in ventilation will almost immediately give rise to a precipitous drop in the carbon dioxide level.
An increasingly popular alternative to general anesthesia is Monitored Anesthesia Care (MAC) with sedation. It differs from general anesthesia in that (a) much shorter-acting anesthetics (e.g., propofol or midazalam) are used to place the patient in a deep state of anesthesia, and (b) the patient is not put on a ventilator, i.e., the patient breathes by himself, just as if sleeping. Though shorter acting, MAC drugs are nonetheless potent hypnotics and analgesics. With the ever-increasing number of out-patient surgeries, many types of surgical procedures that were formerly performed under general anesthesia are now performed using this newer technique. In administering these drugs, it will be appreciated that the anesthetist must be highly skilled in airway management and especially attentive to the patient's breathing since, as noted, the patient is required to breath on his own.
During MAC anesthesia procedures, oxygen is commonly delivered to the patient either through a facial mask or through a nasal cannula. Either of such delivery devices enables the patient to achieve maximum oxygenation. As in the case of general anesthesia, oxygen saturation is typically measured by pulse oximetry, using an infrared sensor which is usually attached to the patient's finger, ear or toe. When a mask is used for administering oxygen, the level of expired carbon dioxide can be easily monitored by placing a capnograph sample line inside the mask. When a nasal cannula is used for administering oxygen, one of the two nasal prongs can be connected to the capnograph sample line while the other prong supplies oxygen. While both of these devices (i.e. the facial mask and nasal cannula) can be highly effective in delivering oxygen and monitoring expired gas, both can be problematic under certain circumstances. For example, a facial mask can interfere with most surgical procedures involving the patient's face and, hence, is usually not used during such procedures. On the other hand, a split nasal cannula can only be used when both nasal passages are clear and the patient is not breathing through the mouth. When either nasal passage is closed or even partially obstructed, either oxygen delivery or carbon dioxide monitoring is compromised. Thus, it is apparent that a need exists for a device that is capable of delivering oxygen and/or monitoring the level of expired gas without presenting the problems identified.
During MAC with sedation procedures, a patient may become so sedate that breathing will become slow or even stop all together. When a respiration failure is detected (as may also occur during an obstruction or closure of the patient's airway, e.g. by the patient's tongue falling back in the pharynx), the anesthetist must be quick to respond. Usually, proper breathing can be restored by a simple jaw thrust or a repositioning of the patient's head. But sometimes a mechanical "airway" must be inserted into the patient's pharynx, either through the mouth or nose, to clear the obstruction and restore proper breathing. A typical mechanical airway comprises a soft rubber tube having a length sufficient to pass any obstruction in the pharynx and to allow normal respiratory gas exchange through the tube. Usually, such airways have an arcuate shape to conform to the shape of the alimentary canal. While being adapted to maintain an open, unobstructed air passage, conventional airways are not adapted to deliver oxygen or the like, or to monitor the level of exhalant gas. In fact, when a facial mask is used to administer oxygen and to sense the carbon dioxide level, the anesthetist must be quick to reapply such mask after removing it to insert a mechanical airway so as to assure continuous blood oxygenation and carbon dioxide monitoring.